Combined cycle power plant

ABSTRACT

The invention relates to a combined cycle power plant that includes, a gas turbine plant, a heat recovery steam generator heated by hot waste gases of a gas turbine plant, and a steam turbine plant driven by the steam produced, and a waste gas purification plant, arranged downstream of the heat recovery steam generator in which carbon oxides in the waste gases can be absorbed by an absorber fluid, which is subsequently regenerated at an elevated temperature in a regenerating section while giving up the carbon oxides for supplying to a storage. The regenerating section has a heater for maintaining a necessary elevated temperature for regeneration. The heater operates with steam from the heat recovery steam generator or from the steam turbine plant. The steam condenses and the resulting hot condensate can be supplied to a flash boiler where it, at low pressure, immediately at least partially evaporates. This steam can be supplied to an appropriate stage of the steam turbine plant according to the steam pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT/EP2013/055881 filed Mar. 21,2013, which claims priority to European application 12160585.1 filedMar. 21, 2012 and European application 12185806.2 filed Sep. 25, 2012,all of which are hereby incorporated in their entireties.

TECHNICAL FIELD

The present invention relates to a combined cycle power plant (CCPP)comprising a gas turbine plant, a heat recovery steam generator (HRSG)heated with hot exhaust gases from the gas turbine plant, and a steamturbine plant driven by the generated steam.

BACKGROUND

Such a CCPP is shown in U.S. Pat. No. 5,839,269. In this known CCPP asteam turbine plant is provided with a high pressure turbine, a mediumpressure turbine and a low pressure turbine, whereby high pressure andmedium pressure steam is produced in the steam generator for driving thehigh pressure or medium pressure turbine, and the steam expanded in themedium pressure turbine is used to drive the low pressure turbine. Inthe CCPP of U.S. Pat. No. 5,839,269 it is also provided that steam withreduced low pressure can be channeled off from a sufficiently hot feedwater tank of the steam generator and fed into a medium stage of the lowpressure turbine through appropriate steam inlets.

In addition U.S. Pat. No. 5,839,269 discloses a range of measures foroptimizing the design of gas turbine plants and for optimizing theoperation of gas turbines.

Gas turbine plants and other large combustion plants are typicallyoperated with fuels based on hydrocarbons. This inevitably generatescarbon oxides during operation, especially carbon dioxide, which is agreen house gas and harmful to the environment, and should therefore beseparated from the waste gases of the gas turbine plant. In principle,known waste gas purification plants can be used which are arrangeddownstream of the respective combustion process and which have anabsorbing section and a regenerating section. Carbon dioxide which iscarried along within the absorbing section, through which the particularwaste gases are flowing, can be absorbed at relatively low temperatureusing an amine-H₂O-system with the formation of a relativelyconcentrated amine carbonate solution. The concentrated amine carbonatesolution can be subsequently converted in a regeneration section at hightemperature into a relatively weak concentrationamine-carbonate-solution, whereby carbon dioxide is released and ledaway and subsequently collected and stored. In lieu of such aminesystems other waste gas purification systems, for example systems usingchilled ammonia, can also be used.

From US 2011/0314815 A1 it is generally known to equip a CCPP asdescribed above with a downstream waste gas purification plant. in US2011/0314815 A1 it is shown that a waste gas purification plant withrelatively small capacity can be sufficient, if the gas turbine plant isoperated with exhaust gas recirculation in such a way that duringcombustion substantially only completely oxidized hydrocarbons, that is,carbon dioxide and water (and N₂) remain. Otherwise, there is noindication towards an optimal integration of the waste gas purificationplant into a CCPP.

SUMMARY

The purpose of the invention is thereby to connect a CCPP with a wastegas purification plant in an optimized way to supply the necessarythermal energy for heating the regeneration section of the purificationplant and to use the residual heat for increasing the performance of thesteam turbine plant.

In particular, according to the invention, a waste gas purificationplant is provided downstream of the gas turbine plant and the heatrecovery steam generation plant, the gas purification plant comprisingan absorbing section and a regenerating section, whereby inside theabsorbing section, through which the waste gases flow, carbon dioxidewhich is carried in the waste gases is absorbed by an amine-H₂O-systemat relatively low temperature forming (relatively) high concentrationsof amine carbonate solution, and whereby the concentrated aminecarbonate solution is converted into a relatively weak amine carbonatesolution in the regeneration section at an elevated temperature givingoff carbon dioxide which is led away, whereby the regeneration sectioncan be heated with steam, and the relatively weak amine carbonatesolution generated in the regeneration section having an elevatedtemperature can be supplied via a heat exchanger back into the absorbingsection for reuse, and thermal energy can be exchanged in the heatexchanger between the relatively weak concentration of amine carbonatesolution and the relatively high concentration of amine carbonatesolution being supplied to the regeneration section.

According to a first aspect of the invention the heat for theregeneration of the amine solution is introduced into the regenerationsection by way of steam from the steam turbine and/or the steamgenerator, and the heat from the regenerated amine solution, having anelevated temperature, is used for preheating the high concentrationamine carbonate solution led away from the absorbing section. Thethermal energy required for regeneration of the amine solution canthereby be substantially reduced.

According to a preferred embodiment, the regeneration section is heatedwith saturated steam at a specified temperature. It is advantageous thatthe temperature level is only dependent on the steam pressure, so thatthe desired temperature can be regulated with the steam pressure.

In the case of a steam turbine plant with a high pressure steam turbine,a medium pressure steam turbine and a low pressure steam turbine, thesteam for heating the regeneration section can be taken from theconnection between the outlet of the medium pressure turbine and theinlet of the low pressure turbine.

According to an advantageous embodiment of the invention, the hotcondensate generated from heating the regeneration section can besupplied to an evaporator of the heat recovery steam generator in orderto produce additional steam with low pressure, the steam can then besupplied to a stage of the low pressure turbine, whereby this steam can,if necessary, be channeled through a superheater of the steam generatorbefore being introduced into the low pressure turbine, in order toincrease its power output.

Advantageously, the thermal energy, which may need to be conducted awayfrom the absorbing section, can be used to preheat the feed water forthe steam generator.

The steam circuits therefore only need to be slightly modified,according to the invention, to supply the necessary thermal energy forthe waste gas purification plant and/or to use resulting residual heatfor increasing the performance of the steam turbine plant, i.e. the hotcondensate is used in a new, additional pressure level (compared to thestandard water-steam cycle.

According to a particularly advantageous embodiment of the invention theregeneration of the amine solution in the regeneration section can becarried out at a temperature of 126° C. as opposed to a possible processtemperature of about 145° C., whereby the separation of the carbondioxide out of the high concentration amine carbonate solution suppliedto the regeneration section happens at a less than optimal processtemperature. This is accepted here because the necessary thermal energyfor heating the regeneration section is thereby disproportionallyreduced, so that the performance of the CCPP and its efficiency can besubstantially increased. As a result, only a relatively small loss ofperformance must be tolerated compared to a CCPP without downstreamwaste gas purification.

According to another aspect of the invention the hot condensate orpressurized water is supplied to at least one flash evaporator andallowed at least partly to evaporate there at low pressure so thatadditional steam is released for operating the steam turbine plant, inparticular for the low pressure steam turbine of the steam turbineplant.

Usable steam for operating the low pressure turbine of the steam turbineplant is produced with little effort by introducing hot condensate orpressurized water into the at least one flash boiler, where it boils dueto a fast reduction in pressure and evaporates. The physical effect isthereby exploited whereby the boiling point of a liquid is dependent onpressure, and accordingly a hot liquid starts to boil suddenly when itis introduced into a space having low pressure and therefore at leastpartially evaporates.

According to a preferred embodiment of the invention, where appropriate,a series of flash boilers can be provided, whereby pressurized water orcondensate from a first flash boiler is supplied to a second flashboiler which has a lower inner pressure compared to the first flashboiler, so that the pressurized water or condensate, coming out of thefirst flash boiler, can at least partially evaporate here. If necessary,further flash boilers can be arranged in a cascade. The flash boilers inthe flash boiler cascade thereby produce steam with accordinglydifferent pressure levels, whereby the steam of each flash boiler issupplied to an appropriate stage of the turbine, in particular to thelow pressure turbine of the steam turbine plant.

The steam coming from a flash boiler can, if necessary, be superheatedwith the heat recovery steam generator plant of the CCPP in order todrive the respective turbine section more effectively.

Preferred features of the invention can be found in the claims and inthe following description of the drawings by way of which particularlypreferred embodiments of the invention are described in more detail.

Protection is not only claimed for the indicated or shown combination offeatures but also for any combination of the shown or indicatedindividual features.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show in:

FIG. 1 a highly schematized representation of a CCPP according to theinvention,

FIG. 2 a schematized representation of a waste gas purification plantaccording to the invention,

FIG. 3 a representation of an advantageous connection of theregeneration section of the waste gas purification plant to a CCPP orits steam generator or its low pressure steam turbine of the steamturbine plant

FIG. 4 a schematized representations for the use of a hot condensate orpressurized water from the power plant or waste gas purification plant,and

FIG. 5 an advantageous variation of the arrangement shown in FIG. 3.

DETAILED DESCRIPTION

According to FIG. 1 the CCPP according to the invention comprises a gasturbine plant 1, which can have a generally known construction, forexample as in the above mentioned U.S. Pat. No. 5,839,269, and having acompressor 11, at least one combustion chamber 12 and a gas turbine 13.The hot waste gases 100 of the gas turbine plant 1 then flow through aheat recovery steam generator 2. Arranged downstream of the heatrecovery steam generator 2 is a waste gas purification plant 4, which isdescribed below. The steam produced in the heat recovery steam generator2 drives a steam turbine plant 5. The gas turbine plant 1 and the steamturbine plant 5 can drive generators 3 or the like respectively, wherebyit is possible in principle to couple the rotor shafts R of the gasturbine plant 1 with those of the steam turbine plant 5 and use a commongenerator 3.

For driving the steam turbine plant 5 a steam circuit can be provided asdescribed in the following:

Water is fed by a pump 7 from a feed water tank 6 into a heater 8, whichis arranged inside of a heat recovery steam generator 2 in the waste gaspath. At the outlet of the heater 8 there is high pressure water with,for example, a pressure of 160 bar and a temperature of 300° C. In atube register 9 downstream of the heater 8 the high pressure water isevaporated and superheated, so that high pressure steam is available atthe outlet of the tube register 9. This superheated, high pressure steamis supplied to a high pressure steam turbine 51 of the steam turbineplant 5, whereby the high pressure steam expands inside the highpressure turbine 51. The steam expanded in this way, CRH (Cold Reheat),is subsequently supplied through a further tube register 10, so thatthis steam is reheated. The steam from the tube register 10 is suppliedto a medium pressure turbine 52 of the steam turbine plant 5, wherebythe steam expands in the medium pressure turbine 52 so that there is lowpressure steam downstream of it, which, if necessary, can be furtherheated in a tube register (not shown) and supplied to a low pressureturbine 53 of the steam turbine plant 5. The steam expanded in the lowpressure turbine 53 subsequently flows into an air- or water-cooledcondenser 109. The condensate produced there is then supplied by a pump111 back to the feed water tank 6.

According to FIG. 2, the waste gas purification plant 4 comprises anabsorbing section 41 through which the waste gas flows, and aregeneration section 42 in order to regenerate the absorbing medium fromsection 41 and to supply it back to the absorbing section 41. At theoutlet of the absorbing section 41 there are waste gases 1000 free ofcarbon oxides.

Inside the absorbing section 41 the waste gases 100 flow through a bathof water and amine solution, whereby the carbon dioxide in the wastegases 100 is bonded by the water to form carbonic acid, which with theamines then forms a relatively high concentration of amine carbonatesolution. This relatively high concentration of amine carbonate solutionis supplied to the regeneration section 42 by a pump 113. Inside theregeneration section 42 a high temperature is maintained, for example atemperature from about 120° to 145° C., at which the relatively highconcentration of amine carbonate solution is converted into a relativelyweak concentration of amine carbonate solution, giving off carbondioxide in the process, whereby the carbon dioxide is supplied by acompressor 114 to a store or the like (not shown).

The temperature necessary for the regeneration process in theregeneration section 42 can be maintained by circulating the relativelyweak concentration of amine carbonate solution, produced in theregeneration section 42, in a circuit through a heater 115, which isitself heated with steam as described below.

The relatively weak concentration of amine carbonate solution issupplied back to the absorbing section 41 by a pump 116, whereby onreturning the solution flows through a heat exchanger 112 through whichthe relatively high concentration of amine carbonate solution beingsupplied to the regeneration section 42 also flows (in oppositedirections), so that the high concentration of amine carbonate solutionsupplied to the regeneration section 42 is pre-heated and the heater 115requires a relatively low thermal input for maintaining the necessarytemperature for the regeneration process.

The heater 115 of the regeneration section 42 is preferably heated withsteam, in particular saturated steam, which can be diverted off at pointA in FIG. 1 in the steam path between the medium pressure steam turbine52 and the low pressure steam turbine 53 of the steam turbine plant 5.This channeled off steam condenses at or in the heater 115 whilst givingup heat to the relatively low concentration amine carbonate solution.The thereby generated condensate K, the temperature of which is aroundthe operating temperature of the regeneration section 42, i.e. at atemperature between about 120° C. and 145° C., can then be suppliedaccording to FIG. 3 to an evaporator 118 and therein heated with heatfrom the heat recovery steam generator 2. The steam generated there, thepressure of which is below the pressure of the steam supplied to theinlet of the low pressure steam turbine, can be subsequently superheatedand supplied via appropriate steam inlets to an intermediate stage ofthe low pressure steam turbine 53.

Alternatively, the steam produced by the evaporator 118 can be suppliedto the heater 115 together with the steam channeled off from point A,preferably superheated. The dotted line in FIG. 3 shows such option.

Alternatively, the condensate K from the heater 115 can also beintroduced into the feed water tank 6 so that, on the one hand, the feedwater is accordingly heated.

As a result the condensate K from the heater 115 is used for producingsteam having a very low pressure for introducing into an intermediatestage of the low pressure steam turbine 53. The waste gas purificationplant is therefore used to generate a fourth steam pressure level, inaddition to the steam pressure levels for the high, middle, and lowpressure steam turbines of the steam turbine plant 5. The steam turbineplant 5 and the heat recovery steam generator 2 are only slightlymodified by the waste gas purification plant 4.

It has proved advantageously to operate the regeneration section 42 ofthe waste gas purification plant 4 at a relatively low temperature,which is actually suboptimal for the regeneration process. The thermalenergy requirement of the heater 115 is thereby disproportionallyreduced, with the result that the loss of performance of the CCPP, dueto the necessary removal of thermal energy during the operation of thewaste gas purification plant 4, is kept low.

The absorbing section 41 of the waste gas purification plant, throughwhich the hot waste gases 100 flow, must be cooled in order to maintainthe necessary low temperature for the absorption process. Thistemperature is about 40° C. in case of the amine system, and about 5° C.in case of the chilled ammonia process.

According to an embodiment, shown in FIG. 4, the hot condensate K fromheater 115 is supplied by a pump 116 to the inlet of a flash boiler 117,whereby a regulating valve 118 is arranged at the inlet of the flashboiler 117 in order to maintain a pressure in the line between the flashboiler 117 and the pump 116, whereby the pressure is above the boilingpressure of water at the prevailing temperature of the condensate K. Inthe flash boiler 117 there is a lower pressure compared to the pressurein the line between the pump 116 and the flash boiler 117, so that thecondensate K introduced into the flash boiler 117, to a greater or lessextent, immediately evaporates (flashes to steam). The very low pressuresteam produced, the pressure of which is below the steam pressure at Ain the steam path between the medium pressure turbine and the lowpressure turbine, can now be supplied to an intermediate stage of thelow pressure turbine 53. By increasing the pressure of the hotcondensate K using pump 116, the pressure and the quantity of theflashed steam, produced in the boiler 117, can be increased.

According to a preferred variation of this embodiment the very lowpressure steam from the flash boiler 117 can be superheated in a heater119 before it is introduced into the low pressure turbine 53. The heater119 can itself be heated with steam from the outlet of the high pressureturbine (CRH) or preferably by flue gas in the heat recovery steamgenerator (HRSG). In principle any other heat source could also be used.

According to another embodiment of the invention, as shown in FIG. 5, inplace of a single flash boiler 117, there can be a cascade of flashboilers 117, 117′, 117″, whereby the condensate coming from each flashboiler 117, 117′ is supplied to a subsequent flash boiler 117′, 117″through a further regulating valve 118′, 118″, whereby the pressure inthe subsequent flash boiler 117′, 117″ is lower than the pressure in thepreceding flash boiler 117, 117′, so that the condensate supplied to itpartially evaporates quickly. For example, the cascade may comprisethree flash boilers 117, 117′, 117″, as shown in FIG. 5.

As mentioned above, the pump 116 in FIGS. 4 and 5 can be used forincreasing the hot condensate (K) pressure, so as to increase thepressure and quantity of the flashed steam.

In this way, steam flows having subsequently decreasing pressures can bedirected from the flash boilers of the flash boiler cascade 117, 117′,117″ and be supplied to appropriate different stages of the low pressuresteam turbine 53.

In this embodiment the steam flows, supplied to the low pressure steamturbine, can also be superheated in appropriate heaters 119, before theyare introduced into the low pressure steam turbine 53. The heater 119may be heated by steam from any suitable source.

This embodiment is based on the general idea that condensed waterexiting at relatively high temperature can be (partially) evaporated inflash boilers at low pressure, and the steam produced can be used fordriving the steam turbine.

1. A combined cycle power plant (CCPP) comprising, a gas turbine plant,a heat recovery steam generator through which hot waste gases from thegas turbine plant flow, a steam turbine plant driven by steam from theheat recovery steam generator, and a waste gas purification plant,arranged downstream of the heat recovery steam generator, having anabsorbing section in which carbon dioxide in the waste gases is absorbedby an absorber fluid, whereby the waste gas purification plant comprisesa regeneration section which is supplied with the absorber fluid loadedwith carbon dioxide, whereby the absorber fluid can be regenerated at anelevated temperature while giving up the carbon dioxide for supplying toa storage, and whereby the regenerated absorber fluid is supplied backinto the absorbing section for absorbing the carbon dioxide in the wastegases, whereby the regeneration section comprises a heater which isheatable with the steam from the heat recovery steam generator or fromthe steam turbine plant, whereby the supplied steam condenses in or atthe heater and the resulting hot condensate is supplied to at least oneevaporator, where it is at least partially evaporated to steam andwhereby this steam is introduced into a stage of the steam turbineplant, in particular into an intermediate stage of the low pressureturbine of the steam turbine plant.
 2. The combined cycle power plantaccording to claim 1, further comprising a heat exchanger is arrangedbetween the absorber section and the regeneration section, whereby theabsorber fluid from the regeneration section being led back into theabsorbing section, and the absorber fluid from the absorbing sectionbeing supplied to the regeneration section through the heat exchanger.3. The combined cycle power plant according to claim 1, wherein thethermal energy extracted from the absorbing section is used forpreheating fuel for the gas turbine plant or for preheating feed waterfor the steam turbine plant.
 4. The combined cycle power plant accordingto claim 1, wherein a part of the steam generated by the at least oneevaporator is added to the steam supplied to the heater of theregeneration section.
 5. The combined cycle power plant according toclaim 1, wherein the steam generated by the at least one evaporator issuperheated in a heater of the heat recovery steam generator and thensupplied to a middle stage of the low pressure turbine of the steamturbine plant.
 6. The combined cycle power plant according to claim 1,wherein the steam turbine plant comprises a high pressure steam turbine,a medium pressure steam turbine and a low pressure steam turbine,whereby steam is taken from a point between the outlet of the mediumpressure steam turbine and the inlet of the low pressure steam turbinefor heating the heater of the regeneration section.
 7. The combinedcycle power plant according to claim 1, wherein the condensate issupplied to a cascade of flash boilers, whereby pressurized water orcondensate from a first flash boiler is supplied to a second flashboiler which has a lower inner pressure relative to the first flashboiler, so that the pressurized water or condensate from the first flashboiler can at least partially evaporate, whereby the steam produced bythe flash boilers is supplied to one or more stages of the steam turbineplant, in particular to the low pressure steam turbine, corresponding totheir different pressures.
 8. The combined cycle power plant accordingto claim 7, wherein the steam from the at least one flash boiler issuperheated, e.g. with the heat recovery steam generator, before beingintroduced into a stage of the steam turbine plant.
 9. The combinedcycle power plant according to claim 7, wherein the steam from the atleast one flash boiler is superheated by the steam, coming from theoutlet of the high pressure steam turbine of the steam turbine plant.10. The combined cycle power plant according to claim 1, wherein theremaining condensate from the at least one evaporator is supplied to thefeed water tank of the steam turbine plant.